1.When Harry saw Voldemort drinking unicorn's blood in the Forbidden Forest, we were unknowingly given a hint of what was to come.

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Firenze, the centaur, describes the process to Harry: "Only one who has nothing to lose, and everything to gain, would commit such a crime. The blood of a unicorn will keep you alive, even if you are an inch from death, but at a terrible price. You have slain something pure and defenceless to save yourself and you will have but a half life, a cursed life, from the moment the blood touches your lips."

These words sound more than familiar when you read Half-Blood Prince and find out about Voldemort's Horcruxes.

2.There were suggestions that Snape was able to read minds as early as the first book.

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In the first book, when Harry believes Snape is responsible for trying to steal the Philosopher's Stone, he worries that Snape knows what he, Ron, and Hermione are up to because he has "the horrible feeling that Snape could read minds".

Later in the series, we find out that Snape is a skilled Legilimens and can, in fact, read minds.

– Tyler Abarca, Facebook

3.Fred and George were trolling Voldemort at age 13 without even knowing it.

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During their Christmas holiday at Hogwarts in Philosopher's Stone, Fred and George got in trouble for "bewitching several snowballs so that they followed Quirrell around, bouncing off the back of his turban".

Little did they know, at the back of Quirrell's turban was none other than Lord Voldemort's face.

4.There's a heartbreaking reason why Dumbledore awarded Neville house points at the end of Philosopher's Stone.

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At the end-of-term feast, Dumbledore awards Neville 10 points because "it takes a great deal of bravery to stand up to our enemies, but just as much to stand up to our friends". We learn later that this is exactly what Dumbledore had to do with Grindelwald.

5.The ~real~ reason why Ron and Neville weren't the best at magic to begin with.

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We all know that Ron and Neville didn't do the best in school, but that wasn't because they lacked the skills to be good wizards. In Deathly Hallows, we learn that using someone else's wand will never produce magic as strong as if you were to use your own – and, in the first few books, Ron is using Percy's old wand and Neville is using his father's.

– Katie Hurt, Facebook

6.The vanishing cabinet that Peeves destroys in Chamber of Secrets has an important role later in the series.

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In Chamber of Secrets, Nearly Headless Nick convinces Peeves to damage a vanishing cabinet in the room above Filch's office to get Harry out of trouble with Filch. The cabinet shows up again in Order of the Phoenix, when Fred and George shove a Slytherin student into it as a prank – but, most importantly, it's the same cabinet that Draco Malfoy repairs in Half-Blood Prince and uses to transport Death Eaters into Hogwarts.

7.Ron's speculation over why Tom Riddle won an award for special services to the school was actually scarily accurate.

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After he spends detention in the trophy room, Ron recognises the name "Tom Riddle" as someone who won an award for special services to the school. After Harry finds his diary, and they're wondering why he won the award, Ron suggests that he may have killed Moaning Myrtle – "that would've done everyone a favour". Of course, it turns out later that Tom Riddle was, in fact, responsible for Myrtle's death – although that's obviously not why he won the award.

8.The Sneakoscope that Ron gifts to Harry isn't actually broken, as they first thought.

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At the beginning of the third book, Ron gives Harry a pocket Sneakoscope as a birthday present. It whistles and spins constantly, and Harry, Ron, and Hermione think it's acting up because it was cheap – but, as we find out later, there actually was someone untrustworthy around them at all times. He was just disguised as a rat.

9.In Prisoner of Azkaban, Professor Trelawney correctly predicts that Dumbledore will be the first person to die.

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There are only a few students and teachers in the Great Hall for Christmas that year – 12, to be exact. When Professor Trelawney is invited to join the table, she at first refuses, saying, "If I join the table, we shall be thirteen! Nothing could be more unlucky! Never forget that when thirteen dine together, the first to rise will be the first to die!"

She eventually does sit down, but the damage has already been done – Ron had Scabbers (aka Peter Pettigrew) in his pocket, which means they had been 13 all along. Dumbledore stood up from the table when he invited Professor Trelawney to join them.

10.And this prediction repeats two more times throughout the series: once with Sirius, and once with Remus.

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Thirteen members of the Order of the Phoenix dine at Grimmauld Place at the beginning of the fifth book. Sirius was the first to rise from the table, and he was the first of them to die.

In Deathly Hallows, after the Order transfer Harry from Privet Drive to the Burrow, there are thirteen people remaining after Moody is killed. They all gather and raise a toast to him – and Remus Lupin gets up to leave first.

11.The early hint that Trelawney may not have been a fraud.

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In Prisoner of Azkaban, Professor Trelawney seems to make a prophecy to Harry in which she says that Voldemort will be reunited with his most loyal servant. When Harry tells Dumbledore about it, Dumbledore says, "That brings her total of real predictions up to two". Of course, we find out two books later that her first real prediction was the one regarding Harry and Lord Voldemort.

12.When Harry is attacked by Dementors and hears his parents' final moments, it's not actually his memory at all.

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Throughout the series, whenever Harry faces the Dementors, he is forced to relive his parents' last moments alive through his memories. However, thinking logically, Harry was only a baby when his parents died and wouldn't have any clear memory of that night. We also learn in Deathly Hallows that Harry has carried a piece of Voldemort's soul with him since that night. So the logical conclusion is that Harry is actually reliving Voldemort's worst memory – of the night he came the closest he ever had to death.

13.And, similarly, Trelawney wasn't entirely wrong when she asked Harry if he was born in mid-winter.

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During a Divination lesson in Goblet of Fire, Professor Trelawney attempts to guess when Harry was born: "Your dark hair… your mean stature… tragic losses so young in life… I think I am right in saying, my dear, that you were born in mid-winter?"

We all know that Harry was born on 31st July – as far from mid-winter as it's possible to get – but Voldemort was born on 31st December, which is most definitely mid-winter.

– Amy Joyce, Facebook

14.The very first chapter of Goblet of Fire contains the most subtle suggestion of what's to come.

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When the gardener Frank Bryce eavesdrops on Voldemort in the Riddle house at the beginning of the fourth book, he hears Voldemort tell Wormtail that if he is loyal, he will be allowed to perform "an essential task ... one that many of my followers would give their right hands to perform".

Later, when Voldemort is brought back to his human(-ish) form, Wormtail cuts off his own right hand in order to complete the process.

They're supposed to be doing their homework, but because they're Harry and Ron, they can't be bothered to actually learn anything. They decide to make up some horrible predictions, and end up accurately predicting Harry's journey through the Triwizard Tournament.

First, Harry says he's "in danger of burns", which happens with the dragons in the first task. Then, Ron says he'll "lose a treasured possession", and each of the champions has a friend ~taken~ from them during the second task. Then they say he'll be "stabbed in the back by a friend" – aka the fake Professor Moody – and that he'll "come off worse in a fight", when Voldemort returns.

16.Dumbledore's reaction to Voldemort's return didn't seem to make much sense – until later.

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When Dumbledore discovers that Harry had a role in bringing Voldemort back to his human form, "Harry thought he saw a gleam of something like triumph in Dumbledore’s eyes". This doesn't seem to make much sense – until we learn, later, that the fact that Harry's blood runs through Voldemort's veins means that Harry is able to survive and defeat him in Deathly Hallows.

17.There was a subtle mention of Mrs Figg at the end of Goblet of Fire.

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We're first introduced to Arabella Figg in Philosopher's Stone as the old lady Harry stays with when the Dursleys are out having fun without him. She returns again in Order of the Phoenix, and we find out she had been there on Dumbledore's orders all along – but there's a hint to her return before that, at the very end of Goblet of Fire. When Harry is in the hospital wing, surrounded by members of the Order, Dumbledore tells Sirius: "You are to alert Remus Lupin, Arabella Figg, Mundungus Fletcher — the old crowd."

– Amanda Rochon, Facebook

18.There's a suggestion of Snape and Lily's story as early as the fifth book – we just didn't notice it.

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When Dudley is attacked by Dementors in the first chapter of Order of the Phoenix, Petunia Dursley shows an unexpected knowledge of the creatures. When Harry asks how she knows about them, she explains, "I heard – that awful boy – telling her about them – years ago".

Of course, we were supposed to think she meant James – but we find out two books later that she was ~actually~ referring to Severus Snape.

– Molly Sloane, Facebook

19.They find the locket Horcrux in Order of the Phoenix, but because they don't realise, they just throw it away.

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When Harry arrives at Grimmauld Place, he and the younger members of the (kind of) Order are tasked with cleaning headquarters while the adults work. While cleaning out the drawing room, they find a bunch of creepy-looking stuff, including "a heavy locket that none of them could open" – which, of course, turns out to be the Horcrux that Regulus was unable to destroy.

20.It's just a tiny thing, but there's a hidden message in the code for the visitor's entrance at the Ministry of Magic.

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You simply get into a seemingly abandoned phone booth and type in 62442 – which, on an old-school phone keypad, spells out "MAGIC".

– Barbara Speck, Facebook

21.There's a hidden meaning behind all those smashed prophecies in the Department of Mysteries.

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When Harry and his friends are attacked by the Death Eaters in the Hall of Prophecies, a couple of them fall from their shelves and smash on the floor. Only a small amount of what they held could be heard over Lucius Malfoy's voice, but what ~is~ heard is: "...at the Solstice will come a new...and none will come after..."

The title of the final book in the series, Harry Potter and the Deathly Hallows, was announced on 21st December 2006 – the Winter Solstice.

22.The tiara Harry used to mark his hidden potions book in Half-Blood Prince would turn out to be incredibly important one book later.

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Just like the locket, the diadem Horcrux showed up earlier in the series, when Harry hid his potions textbook in the Room of Requirement underneath a chipped bust of an ugly wizard – on top of which he "perched a dusty old wig and a tarnished tiara ... to make it more distinctive".

23.The story of how Fred and George got their names.

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Almost all of the Weasleys are named after past monarchs of Britain, but Fred and George are particularly interesting – George is named for King George III, who went deaf in his later years, and who became heir to the throne after the untimely death of his father, Prince Frederick of Wales.

Of course, names are a huge part of Harry Potter – Sirius is named after the Dog Star, and Remus Lupin's name is basically Wolfy McMoonface.

24.In Deathly Hallows, we finally get confirmation that Neville Longbottom belonged in Gryffindor all along.

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Towards the end of the final book, we see Neville kill Voldemort's snake, Nagini – and therefore the final Horcrux – using the sword of Gryffindor. However, we know from Chamber of Secrets that "only a true Gryffindor" could pull the sword out of the Sorting Hat. Neville – who had worried for years that he was misplaced in Gryffindor house – was, after all, a true Gryffindor.

25.And we ~finally~ understand the incredibly important meaning behind Ollivander's insistence that "the wand chooses the wizard".

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In the final book – six years after Harry first visits Mr Ollivander and hears the phrase "the wand chooses the wizard" – he defeats Voldemort, who attempts to kill Harry with a wand that rightfully belongs to him. When Harry's spell collided with Voldemort's, the Elder Wand flew out of Voldemort's hand and flew "through the air toward the master it would not kill, who had come to take full possession of it at last".